b1 and 2 cell structure and support

eukaryotes and prokaryotes

eukaryotes and prokaryotes

Plant and animal cells (eukaryotic cells) have a cell membrane, cytoplasm and genetic material enclosed in a nucleus. eukaryotic cellular complex multicellular organisms

Bacterial cells (prokaryotic cells) are much smaller in comparison and unicellular. They have cytoplasm and a cell membrane surrounded by a cell wall. The genetic material is not enclosed in a nucleus. It is a single DNA loop and there may be one or more small rings of DNA called plasmids.

Animal and plant cells features

Most animal cells have the following parts:

• a nucleus controls the activities of the cells

• cytoplasm mainly water that holds the ribosomes

• a cell membrane surrounds the cell and controls what goes in and out. glucose and oxygen in carbon dioxide out via diffusion

• mitochondria small organelle which are the site of respiration. they have folds that increase the surface area to volume ratio making them more efficient

• ribosomes site of protein synthesis

In addition to the parts found in animal cells, plant cells often have: • chloroplasts needed for photosynthesis and produce chlorophyll

• a permanent vacuole filled with cell sap keeping the cell turgid and strong

Plant and algal cells also have a cell wall made of cellulose, which strengthens the cell.

cell specialisation

Cells may be specialised to carry out a particular function:

• nerve cells they have a long fibre (axon) so they can carry messages up and down the body over long distances

• in a stimulated neuron, an electrical nerve impulse passes along the axon

• the axon is insulated by a fatty (myelin) sheath - the fatty sheath increases the speed of the nerve impulses along the neuron

• at each end of the neuron are tiny branches (dendrons), which branch even further into dendrites - the dendrites receive incoming nerve impulses from other neurons

muscle cells have lots of mitochondria for contraction and relaxation. contain filaments of protein that slide over each other to cause muscle contraction.

• root hair cells large surface area to volume ratio to absorb as much water and minerals as possible.they also have lots of mitochondria for the active transport of minerals

xylem dead There are no top and bottom walls between xylem vessels, so there is a continuous column of water running through them. Their walls become thickened and woody. They therefore support the plant.

phloem live cells in plants that have sieve plates Dissolved sugars and amino acids can be transported both up and down the stem. Companion cells, adjacent to the sieve tubes provide energy required to transport substances in the phloem.

adaptations of sperm

• Its role is to deliver genetic material to an egg cell to fertilise it

• It has half as much genetic material as a normal cell, so that the sperm and egg together will have the normal amount

• It has lots of mitochondria to provide the energy for movement

• It has a flagellum to allow it to swim to reach the egg

• It is streamlined to make swimming easier

• It has digestive enzymes in its head to break through the wall of the egg

Give two drawbacks of using embryonic stems cells in stem cell therapy.

model answer:The embryonic stem cells must come from embryos. These are in limited supply, and some people have ethical objections to it, as they think the embryos could have developed into a person.The cells could be rejected by the person's immune system as it would identify them as foreign.

• Stem cells have a limited supply

• The risk of rejection

• Ethical issues associated with stem cells 

List three factors that affect the rate of diffusion.

Concentration gradient

Temperature

Surface area

Distance to diffuse across (if diffusing across a membrane

Why does a higher temperature increase the rate of diffusion?

• Higher temperature means particles have more (kinetic) energy

• So they move around faster 

• And can diffuse more quickly

Give two examples of exchange surfaces in humans and describe their function.

Example 1 - Alveoli (or lungs)

Example 1 - Alveoli allow oxygen and carbon dioxide to diffuse in and out of the body/bloodstream 

Example 2 - Villi (or small intestines)

Example 2 - Villi allow nutrients such as glucose, amino acids, mineral ions etc to be absorbed from the small intestines into the bloodstream

State and explain three features that most exchange surfaces have in common. 

Feature 1 - Large surface area

Explanation 1 - Lots of molecules can diffuse across at the same time

Feature 2 - Surfaces are very thin

Explanation 2 - Substances only have to diffuse a short distance

Feature 3 - Surfaces are permeable

Explanation 3 - Substances are able to pass through the surface

Feature 4 - Good blood supply (good supply of 'internal medium')

Explanation 4 - Maintains a strong concentration gradient as blood is constantly replaced

Feature 5 - Good supply of 'external medium'

Explanation 5 - Maintains a strong concentration gradient as the air or food etc is constantly replaced

State and explain three features of alveoli that make them good exchange surfaces. 

Feature 1 - There are lots of alveoli, giving a large total surface area

Explanation 1 - Lots of molecules can diffuse across at the same time

Feature 2 - Surfaces are very thin (only 1 alveolar cell and 1 capillary cell thick)

Explanation 2 - Substances only have to diffuse a short distance

Feature 3 - Surfaces are permeable

Explanation 3 - Oxygen and carbon dioxide are able to diffuse across

Feature 4 - Good blood supply (good supply of 'internal medium')

Explanation 4 - Maintains a strong concentration gradient as blood is constantly replaced

Feature 5 - Good supply of air ( good supply of 'external medium')

Explanation 5 - Maintains a strong concentration gradient as the air in the alveoli is constantly replaced with new oxygen rich air from the atmosphere

Cell differentiation

As an organism develops, cells differentiate to form different types of cells.

• Most types of animal cell differentiate at an early stage.

• Many types of plant cells retain the ability to differentiate throughout life. In mature animals, cell division is mainly restricted to repair and replacement. As a cell differentiates it acquires different sub-cellular structures to enable it to carry out a certain function. It has become a specialised cell.

Microscopy

Limited to the differences in magnification and resolution. An electron microscope has much higher magnification and resolving power than a light microscope. This means that it can be used to study cells in much finer detail. This has enabled biologists to see and understand many more sub-cellular structures. formula: magnification = size of image /size of real object

Culturing microorganisms (biology only)

Bacteria multiply by simple cell division (binary fission) as often as once every 20 minutes if they have enough nutrients and a suitable temperature. Bacteria can be grown in a nutrient broth solution or as colonies on an agar gel plate. Uncontaminated cultures of microorganisms are required for investigating the action of disinfectants and antibiotics.

method of culturing microorganisms

Petri dishes and culture media must be sterilised before use

• inoculating loops used to transfer microorganisms to the media must be sterilised by passing them through a flame

• the lid of the Petri dish should be secured with adhesive tape and stored upside down

• in school laboratories, cultures should generally be incubated at 25°C.

chromosomes

The nucleus of a cell contains chromosomes made of DNA molecules. Each chromosome carries a large number of genes. In body cells the chromosomes are normally found in pairs.

cell division

Cells divide in a series of stages called the cell cycle. Students should be able to describe the stages of the cell cycle, including mitosis. During the cell cycle the genetic material is doubled and then divided into two identical cells. Before a cell can divide it needs to grow and increase the number of sub-cellular structures such as ribosomes and mitochondria. The DNA replicates to form two copies of each chromosome. In mitosis one set of chromosomes is pulled to each end of the cell and the nucleus divides. Finally the cytoplasm and cell membranes divide to form two identical cells.

stem cells

A stem cell is an undifferentiated cell of an organism which is capable of giving rise to many more cells of the same type, and from which certain other cells can arise from differentiation. Stem cells from human embryos can be cloned and made to differentiate into most different types of human cells. Stem cells from adult bone marrow can form many types of cells including blood cells. Meristem tissue in plants can differentiate into any type of plant cell, throughout the life of the plant.

Knowledge and understanding of stem cell techniques are not required. Treatment with stem cells may be able to help conditions such as diabetes and paralysis. In therapeutic cloning an embryo is produced with the same genes as the patient. Stem cells from the embryo are not rejected by the patient’s body so they may be used for medical treatment. The use of stem cells has potential risks such as transfer of viral infection, and some people have ethical or religious objections.

Stem cells from meristems in plants can be used to produce clones of plants quickly and economically.

• Rare species can be cloned to protect from extinction.

• Crop plants with special features such as disease resistance can be cloned to produce large numbers of identical plants for farmers.

diffusion

Substances may move into and out of cells across the cell membranes via diffusion. Diffusion is the spreading out of the particles of any substance in solution, or particles of a gas, resulting in a net movement from an area of higher concentration to an area of lower concentration. Some of the substances transported in and out of cells by diffusion are oxygen and carbon dioxide in gas exchange, and of the waste product urea from cells into the blood plasma for excretion in the kidney.

Factors which affect the rate of diffusion are: • the difference in concentrations (concentration gradient) • the temperature • the surface area of the membrane. A single-celled organism has a relatively large surface area to volume ratio. This allows sufficient transport of molecules into and out of the cell to meet the needs of the organism.

exchange surfaces

In multicellular organisms, surfaces and organ systems are specialised for exchanging materials. This is to allow sufficient molecules to be transported into and out of cells for the organism’s needs. The effectiveness of an exchange surface is increased by: • having a large surface area • a membrane that is thin, to provide a short diffusion path • (in animals) having an efficient blood supply • (in animals, for gaseous exchange) being ventilated.

osmosis

Water may move across cell membranes via osmosis. Osmosis is the diffusion of water from a dilute solution to a concentrated solution through a partially permeable membrane.

active transport

Active transport moves substances from a more dilute solution to a more concentrated solution (against a concentration gradient). This requires energy from respiration. Active transport allows mineral ions to be absorbed into plant root hairs from very dilute solutions in the soil. Plants require ions for healthy growth. It also allows sugar molecules to be absorbed from lower concentrations in the gut into the blood which has a higher sugar concentration. Sugar molecules are used for cell respiration. Students should be able to: • describe how substances are transported into and out of cells by diffusion, osmosis and active transport • explain the differences between the three processes.

electron microscopes

use electrons in rays of light to creat an image since electrons are very smaller than visible light higher magnifications can be used .

metod of preparing onion cell to see thorugh microscope

• Use tweezers to peel back a layer of epidermal tissue

• Add a drop of water to a clean slide

• Spread the epidermal tissue out on the slide

• Ensure the tissue is one cell thick

• Add a drop of dye / iodine / stain so structures are visible / clear

• Place a cover slip over the top

• Tap gently to remove air bubbles

• Dab away any excess dye from the slide

why is an under developed root hair cell detrimental to a plant

• The purpose / function of the root hair is to increase surface area; [1 mark]

• For absorption of water (by osmosis); [1 mark]

• (And) for absorption of mineral ions / named example (e.g. magnesium ions, nitrate ions); [1 mark]

• Less root hairs would reduce absorption; [1 mark]

• Water is essential for photosynthesis / maintaining pressure / as a solvent; [1 mark]

• (Reduced absorption) could lead to mineral deficiencies, causing stunted growth / named example of mineral deficiency described; [

an four of

Differentiation plays the following role in producing root hair cells which allow them to carry out their function:

• Differentiation determines cell shape / development of specific organelles (to allow them to carry out a particular function); [1 mark]

• Root cells grow extensions / root hairs to give a large surface area to volume ratio this allows maximum uptake of water by osmosis; [1 mark]

• They also develop many mitochondria to provide energy for active transport of mineral ions; [1 mark]

• A large vacuole for storage of water and minerals to maintain a concentration gradient (for continuous uptake of water by osmosis); [1 mark]

• Root hair cells have no chloroplasts, as they do not photosynthesize; [1 mark]

Starch found in the roots of grass supports growth in the following way:

• Glucose is stored as starch in plants; [1 mark]

• Energy is released from glucose in respiration; [1 mark]

• Energy is required for growth / building of new molecules OR energy is required for active transport of mineral ions / nitrates into the root; [1

mitosis

2 daughter cells are produced

used to help cells reproduce naturally

tutorial:

1. chromosome multiply and line up as the membrane and nucleus dissapear

2. then the copies and original chromosomes move to opposite ends of the cell

3. cell membrane divides(cytokinesis)

4. cells are formed

simalarities between mitosis and meiosis

mitosis produces two (daughter) cells but meiosis produces four (daughter) cells

one cell division in mitosis but two cell divisions in meiosis

mitosis produces cells with two of each chromosome, but meiosis produces cells with one of each chromosome

mitosis produces genetically identical cells, but meiosis produced genetically different cells

simalarities between mitosis and meiosis

DNA doubles / copies / replicates (once)

increase in the number of mitochondria / ribosomes / sub-cellular structures

advantages of asexual reproduction

many offspring produced • takes less time

• (more) energy efficient

• genetically identical offspring allow offspring are clones

• successful traits propagated / maintained / passed on (due to offspring being genetically identical)

• no transfer of gametes or seed dispersal allow no vulnerable embryo stage allow no need for animals

• not wasteful of flowers / pollen / seeds

• colonisation of local area

why is sexual reproduction an advantage

genetic variation (in offspring) 1 (so) better adapted survive allow reference to natural selection or survival of the fittest 1 (and) colonise new areas by seed dispersal

or

can escape adverse event in original area (by living in new area) must imply new area 1 many offspring so higher probability some will survive

stem cells in mammels

stem cells:embryonic and adult stem cells

can differentiate into other types of cells

embryonic stem cells

can differentiate in ANY type of cell and are found in the embryo aka totipotent after this it can change anymore

advantages and disadvantages of embryonic cells

• can create many embryos in a lab

• painless technique

• can treat many diseases / stem cells are pluripotent / can become any type of cell (whereas bone marrow can treat a limited number) embryos disadvantages

• harm / death to embryo

• embryo rights / embryo cannot consent

• unreliable technique / may not work

advanatages nd disadvantage from stem cells collected from bone marrow

bone marrow advantages

• no ethical issues / patient can give permission

• can treat some diseases

• procedure is (relatively) safe / doesn’t kill donor

• tried and tested / reliable technique

• patients recover quickly from procedure

bone marrow disadvantages

• risk of infection from procedure

• can only treat a few diseases

• procedure can be painful both procedures advantage can treat the disease / problem both procedures disadvantages

• risk of transfer of viral infection

• some stem cells can grow out of control / become cancerous

adult stem cells

found in bones

use to repair the body when damaged

they can only differentiate into the type of cells that they are near

they cannot differentiate into any type of stem cell

aka multipotent

example animals with embryonic stem cells throughout their lives

starfish can regrow itself if all its legs are ripped off

lizards can regrow their tail and parts of their body

stem cells in plants

• stem cells can differentiate throughout their whole lives

• found in the meristem

• found at the roots and shoots of plants

• hence cutting can be taken and grow well

• rare plants are grown this way

• e.g roses and orchids

stem cell research

• is an ethical issues

• people disagreee for religous and moral reasons

• religous-jehovas witness

• moral- some thing its bad because the research comes from aborted babies

medical uses of stem cells

• treatment for paralysed patients creating new nerve cells in spinal chord or brain

• treat conditions such as diabetes

• replaces choroid in eye so patient can see

• replace defective organ

how gases/minerals are transferred through the vili and alveoli

asceptic techniques

Aseptic technique is a set of practices that protects patients from healthcare-associated infections and protects healthcare workers from contact with blood, body fluid and body tissue.

in regards to culturing microorganisms they help obtain and pure culture of bacteria

aseptic techniques to use when investigatingculturing microorganisms

Aseptic technique is a set of practices that protects patients from healthcare-associated infections and protects healthcare workers from contact with blood, body fluid and body tissue.

features of nerve cells

• long

• has branches

• has insulation

simalarities between prokaryotic and eukaryotic cells

both have

• cytoplasm

• (cell) membrane

• DNA / genetic material

• ribosomes

substances in growth medium

• glucose / sugars / starch

• amino acids / protein

• hormones allow named hormones e.g. auxin

• ions / minerals allow magnesium / nitrate

• vitamins

• water allow H2O / H2O ignore oxyg

how is mycoprotein produced

fungus / Fusarium

with glucose (syrup

aerobic conditions or in presence of oxygen ignore air

mycoprotein is harvested / purified allow ammonia added (as source of nitrog

adaptations of lungs

(many) alveoli • provide a large(r) surface area (: volume)

• capillaries are thin or alveoli / capillary walls are thin or one cell thick or capillaries are close to the alveoli

• which provides short diffusion path (for oxygen / carbon dioxide)

• breathing (mechanism) moves air in and out or lungs are ventilated

• to bring in (fresh) oxygen

• to remove carbon dioxide • to maintain a concentration / diffusion gradient

• large capillary network (around alveoli) or good blood supply • to remove oxygen(ated blood) quickly

• to bring carbon dioxide to the lungs quickly • to maintain a concentration / diffusion gradient

how ion, water and sugar are transported through a plant

Water: (P) taken up by osmosis • from an area of low to high concentration allow high concentration of water to low concentration of water allow from high water potential to low water potential ignore along a concentration gradient (V) travels in the xylem (M) to the leaves or from the roots / soil (P) transpiration stream • movement replaces water as it evaporates from leaves (V) in the xylem Sugar: (P) made during photosynthesis travels in the phloem (M) to other parts of the plant or to storage organs or travels up and down